Solid state image pickup device and its driving method using two different periods

ABSTRACT

A method and apparatus for driving a solid state image pickup device. The method and apparatus include setting a first signal charging period and a second signal charging period for each one of a plurality of unit pixels. The second signal charging period is shorter than the first signal charging period. A first signal charge is produced during the first signal charging period and a second signal charge is produced during the second signal charging period. It is judged whether the first signal charge is saturated or not saturated. Then based on this judgment an input light amount is determined. The input light amount is determined using only the second signal charge when the first signal charge is saturated. The input light amount is determined using only the first signal charge when the first signal charge is not saturated.

This application is a division of U.S. patent application Ser. No.08/918,424 filed Aug. 26, 1997, now U.S. Pat. No. 6,392,700, which is adivision of U.S. patent application. Ser. No. 08/726,337, filed Oct. 3,1996, now abandoned which is a continuation of U.S. application Ser. No.08/261,841, filed Jun. 17, 1994 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid state image pickup device forexpanding the management range in the quantity of incident light to thehigh-luminance side and a method for driving the same, and inparticular, to a solid state image pickup device for expanding themanagement range of the quantity of incident light by setting up atleast two signal charging periods in the specified period represented bythe field or frame of a video signal and reproducing the signal chargesin the signal charging period without using any external field memory orany frame memory and a method for driving the same.

2. Related Art of the Invention

According to a conventional technique, at least two mutually differentcharging periods are set in one frame or one field in expanding themanagement range in the quantity of incident light. For example, a firstcharging period T1 corresponding to the conventional vertical scanningperiod and a second charging period T2 shorter than the first chargingperiod in the vertical blanking period are set in one field period TF.Then a signal charge Q1 obtained in the first charging period isreproduced with a gain of 1, and a signal charge Q2 obtained in thesecond charging period is reproduced with a gain (T1/T2). As a result,when the signal charge Q1 reaches a saturation charge quantity, amanagement range in quantity of incident light being (T1/T2) timesgreater than the gain in the conventional case is achieved using thesignal information of the signal charge Q2.

In the above-mentioned element drive method for expanding the managementrange in the quantity of incident light, there is a proposal fordispensing with any external frame memory (Japanese Patent Laid-OpenPublication No. SHO 63-250980). The above-mentioned proposal describes amethod for continuously transferring signal charges obtained in twocharging periods separately provided in one field period TF in avertical CCD by producing three signal packets with four pixels and atotal of eight transfer electrodes according to the structure of thecurrent CCD, using signal charges of a mixture of two pixels in thefirst charging period as two packets, and using signal charges of amixture of four pixels in the second charging period as one packet.

SUMMARY OF THE INVENTION

However, it is required to read two times during a time interval of Tfor the purpose of additively mixing the signal charges of the mixtureof four pixels. There exist two different types of signal charges T2 and(T2+T) in an identical packet. When the signal charges of the mixture offour pixels in the two types of charging periods are mutually differentin time by T are subjected to calculation processing with the gain of(T1/T2) without distinction, there occurs disadvantages such asmisalignment in color and misalignment in luminance when adjusting thesecond charging period T2 according to the quantity of light of thesubject.

By using a drive method and solid state image pickup device free of thedifference of T between charging periods in the second charging periodT2 that causes problems when signal charges are read from aphotoelectric converting element to a vertical CCD at least two times inone field period, the management range in the quantity of incident lightcan be expanded. Therefore, misalignment in color and misalignment inluminance can be avoided.

The management range in quantity of incident light can be expanded tothe high-luminance side without using any external field memory or anyframe memory for a subject having a wide range of distribution inluminance by managing the quantity of light smaller than a standardquantity of light and the quantity of light about two times greater thanthe standard quantity of light with the first charging period T1 andmanaging a region having a saturation charge quantity in the firstcharging period T1 with the second charging period T2 in the verticalblanking period.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a solid state image pickup device of thepresent invention.

FIG. 2 is a chart for explaining a first drive method of the presentinvention.

FIG. 3 is a diagram showing an A-field of a first drive embodiment ofthe present invention.

FIG. 4 is a diagram showing a B-field of the first drive embodiment ofthe present invention.

FIG. 5 is a diagram of an exemplified first solid state image pickupdevice of the present invention.

FIG. 6 is a graph for explaining the effect of the first embodiment ofthe present invention.

FIG. 7 is a chart for explaining a second drive method of the presentinvention.

FIG. 8 is a diagram of an A-field of a second drive embodiment of thepresent invention.

FIG. 9 is a diagram of a B-field of the second drive embodiment of thepresent invention.

FIG. 10 is a chart for explaining a third drive method of the presentinvention.

PREFERRED EMBODIMENTS

The following describes an embodiment of the present invention withreference to the drawings.

FIG. 1 shows an exemplified solid state image pickup device relevant tothe claim 1 of the present invention.

Four transfer electrodes of a VCCD 110 correspond to a unit pixel 100,while eight transfer electrodes of V1 transfer electrode 101, V2transfer electrode 102, V3 transfer electrode 103, V4 transfer electrode104, V5 transfer electrode 105, V6 transfer electrode 106, V7 transferelectrode 107, and V8 transfer electrode 108 are used as a total ofeight transfer electrodes which correspond to two continuous unitpixels, when an 8-phase transfer clock is applied to them. The V2transfer electrode 102 and the V6 transfer electrode 106 are eachprovided with a read gate 109. Although two read gates are provided forone read electrode by means of a polysilicon of the first layer, theread electrode may utilize the polysilicon of either the first layer orthe second layer. It is also permitted to consider that adjoining twopixels in the direction of the VCCD as one pixel in the case where theconventional CCD is used. For the element drive examples in FIG. 2 andsubsequent figures, a description is provided based on the structure ofFIG. 1.

FIGS. 2, 3, and 4 show embodiments relevant to the claims 2, 3, and 4 bymeans of the solid state image pickup device shown in FIG. 1.

FIG. 2 shows an A-FIELD 201 and a B-FIELD 203 of a normal TV frame. FIG.2 also shows the timing of charge, read, and transfer of signals in theA-FIELD 201 and B-FIELD 203 in each odd-line pixel and each even-linepixel.

The odd-line pixel 232 and the even-line pixel 233 are preliminarilymade to have charge period start timing which are caused to coincideusing a known electronic shuttering operation (VOD (vertical overflowdrain shuttering operation) sweep).

The even-line pixel 233 obtains an even-line first signal charge 205according to a signal input in a period T11 224. An operation of read tothe VCCD is executed with timing TAF1 210. Meanwhile, the odd-line pixel232 obtains an odd-line first signal charge 206 according to a signalinput in a period T12 225, and an operation of read to the VCCD isexecuted with timing TAF21 211. Further in a V-blank period 202, theeven-line pixel 233 obtains an even-line second signal charge 207according to a signal input in a period T2 227. An operation of read tothe VCCD is executed with timing TAS1 212. Meanwhile, the odd-line pixel232 obtains an odd-line second signal charge 208 according to a signalinput in a period T2 228 set up in an identical charging period with theperiod T2 227, and an operation of read to the VCCD is executed withtiming TAS21 213. As a result, control of the charging times in theperiod T2 227 and the period T2 228 executed for the purpose of pickingup a region having a high luminance of the subject in the V-blank period202 is executed by adjusting a VOD-sweep period 229 provided within theentire field period 226.

Although the same operation is executed in the B-FIELD 203, it ispermitted to replace the charging period of an odd-line first signalcharge 214 with the charging period of an even-line first signal charge215.

FIGS. 3 and 4 show the timing of the read and transfer operations. Asignal charge 240 read with the timing T_(AF1) 210 is transferred in theVCCD by one pixel. With the timing T_(AF21) 211, a signal charge 241 isread. In FIG. 3, twenty clock pulses are used from the timing T_(AF1)210 to the timing T_(AF21) 211. Subsequently, by using twenty clockpulses from the timing T_(AS1) 212 to the timing T_(AS21) 213, thecharging periods of T2 227 and T2 228 are allowed to have the sameduration. Further, a signal charge 242 corresponding to the even-linesecond signal charge 207 and a signal charge 243 corresponding to theodd-line second signal charge 208 are mixed with each other with thetiming T_(AS21) 213 in a manner as shown in FIG. 3. There is an intervalof twenty clock pulses from T_(AS1) 212 to T_(AS21) 213 between theperiods for reading both the signal charges. Subsequently, the signalcharges are transferred in the VCCD according to the 8-phase clock.Although the charging periods T2 227 and T2 228 have a charging periodof twenty clock pulses in this example, it is of course permitted toprovide no limitation on the number of clock pulses. Meanwhile, asdescribed hereinbefore, the charging periods of T2 227 and T2 228 arecontrolled by increasing or decreasing the interval from T_(AF21) 211 toT_(AS1) 212, according to which the VOD-sweep period 229 is increased ordecreased.

FIG. 5 shows an embodiment relevant to the claims 5, 6, and 8. FIG. 6shows the effect of expanding the management range in quantity ofincident light.

Incident light is photo-electrically converted in a one-unit pixelphotoelectric converter section 300. Meanwhile, an electronic shutteringtime two-pixel mixture signal charge 301, a field signal charge 1 302,and a field signal charge 2 303 are transferred respectively by HCCD1304, HCCD2 305, and HCCD3 306. After passing through a CDs & clampcircuit 307, they are subjected to decision of signal saturation by asignal decision circuit 309 based on the saturation or unsaturationcondition of signals output from all or a part of the HCCD 1, 2, and 3.After being further subjected to selection of output in a signalselector circuit 308, they are subjected to calculation processing asdescribed hereinafter in a signal processing circuit 310 to executeimage signal reproduction.

An exemplified image reproducing method is shown. In the followingconditional expressions, VT represents a voltage corresponding to thesaturation charge quantity of an element.

First, when the condition of Equation 1 is true in regard to the signalvoltages V (T1) and V (T12) in the charging periods T11 and T12, thesignals V (T11) and V (T12) are selected by the signal selector circuit308. When the condition of Equation 1 is false, the signal selectorcircuit 308 selects the electronic shuttering time two-pixel mixturesignal charge 301, while the signal voltage in the charging period T2 isconverted into Vsig (T2) in a signal processing circuit 310 throughcalculation of Equation 2. Although a is defined by Equation 3 in thisplace, it is permitted to use another appropriate value, for example,the values in Equation 4. It should be noted that the other signalswhich have not been selected are abandoned.max(V(T 11), V(T 12))<V _(T)  Equation 1Vsig(T 2)=a×V(T 2)  Equation 2:a=T 11/T 2  Equation 3:a=T 12/T 2  Equation 4:

The expansion of the management range in quantity of incident light ofthe present embodiment will be described with reference to FIG. 6.

An output signal charge quantity obtained by the read and transferoperations through mixture of two pixels in a conventional CCD is shownas a conventional two-pixel mixture type saturation electric chargequantity 320. The saturation charges quantity of signal charges in thecharging periods T11 224 and T12 225 shown in FIG. 2 (a) come to have avalue corresponding to one transfer electrode in one unit pixel in oneunit pixel 100 shown in FIG. 1, and therefore the value is one fourth ofthe conventional two-pixel mixture type saturation electric chargequantity. In forming a luminance signal, a signal charge 240 and asignal charge 241 are added together in an external circuit, andtherefore the value is half of the conventional two-pixel mixture typesaturation charge quantity. The value is shown as all pixel independentread time saturation electric charge quantity 321.

According to the element and drive method of the present embodiment, asignal charge obtained by mixing the even-line second signal charge 207in the charging period T2 227 with the odd-line second signal charge 208in the charging period T2 228 can be independently read simultaneously,and therefore an electronic shuttering two-pixel mixing time saturationelectric charge quantity 322 can be obtained. In this place, the periodsT2 227 and T2 228 can be varied, for example, from 1/500 of a second to1/2000 of a second to allow an effect as represented by variable 325 inFIG. 6 to be obtained. Therefore, a management incident light quantityexpansion range 323 greater than a conventional management incidentlight quantity upper limit 324 can be achieved.

FIGS. 7, 8, and 9 show an embodiment in the case where VOD-sweep is notused. FIG. 7 shows an odd-line pixel 432 and an even-line pixel 433 aswell as the timing of signal charge, read, and transfer in an A-FIELD401 and a B-FIELD 403 of a normal TV frame.

In this case, the charging period start timings of the odd-line pixel432 and the even-line pixel 433 differ from each other. The even-linepixel 433 obtains an even-line first signal charge 405 according to asignal input in a period T11 424. An operation of read to the VCCD isexecuted with timing TAF1 410. Meanwhile, the odd-line Pixel 432 obtainsan odd-line first signal charge 406 According to a signal input in aperiod T12 425, and an Operation of read to the VCCD is executed withtiming TAF21 411. Further in a V-blank period 402, the even-line pixel433 obtains an even-line second signal charge 407 according To a signalinput in a period T2 427. An operation of read To the VCCD is executedwith timing TAS1 412. Meanwhile, The odd-line pixel 432 obtains anodd-line second signal Charge 408 according to a signal input in aperiod T2 428 set in an identical charging period with the period T2427, and an operation of read to the VCCD is executed with Timing TAS21413. In this place, the periods T11 424 and T12 425 differ from eachother and also differ depending on whether they are in the A-FIELD 401or in the B-FIELD 403. Therefore, when the periods T2 427 and T2 428having the Same charging time are controlled, there is a possibility ofGenerating misalignment in color and misalignment in Luminance in theperiod of four fields. However, the pixel data are read independently inthe present invention, a calculation (Equation 6) which takes the ratioin charging period (Equation 5) into account can be allowed. Therefore,by using a value Vsig′ (T11) calculated in terms of the charging periodT12, neither misalignment in color nor misalignment in luminance takesplace.b=T 12/T 11  Equation 5:Vsig′(T 11)=b×V(T 11)  Equation 6:

FIGS. 8 and 9 show the timing of the read and transfer operations. Asignal charge 440 read with the timing T_(AF1) 410 is transferred in theVCCD by one pixel. With the timing T_(AF21) 411, a signal charge 441 isread. In FIG. 3, twenty clock pulses are used from the timing T_(AF1)410 to the timing T_(AF21) 411. Subsequently, by aligning the timingfrom T_(AS1) 412 to the timing T_(AS21) 413 in twenty clock pulses, thecharging periods in the period T2 427 and T2 428 are allowed to have anidentical duration. Further, after a signal charge 442 corresponding tothe even-line second signal charge 407 is transferred by one pixel inthe period of twenty clock pulses, a signal charge 443 corresponding tothe odd-line second signal charge 408 is read through superimpositionwith the timing T_(AS21) 412 in a manner as shown in FIG. 3 to be mixedwith the signal charge and subsequently transferred in the VCCDaccording to the 8-phase clock. Although the charging periods T2 427 andT2 428 correspond to twenty clock pulses in this example, it is ofcourse permitted to provide no limitation on the number of clock pulses.

FIG. 10 shows a case where the charging period of an odd-line firstsignal charge 414 and the charging period of an even-line first signalcharge 415 as shown in FIG. 7 are replaced with each other. In thisplace, an even-line first signal charge 505 is a signal charge obtainedfrom a signal input in a period T11 524. An operation of read to theVCCD is executed with timing T_(AF1) 510. An odd-line first signalcharge 506 is a signal charge obtained from a signal input in a periodT12 525, and an operation of read to the VCCD is executed with timingT_(AF2) 511. An even-line second signal charge 507 is a signal obtainedfrom a signal input in a period T2 527. An operation of read to the VCCDis executed with timing T_(AS1) 512. An odd-line second signal charge508 is a signal obtained from a signal input in a period T2 528, and anoperation of read to the VCCD is executed with timing T_(AS2) 513.

In the present invention, the periods T11 524 and T12 525 can be set upat an identical duration, the conversion of Equation 6 is not necessary.

As described above, in the present invention, the management range inquantity of incident light can be expanded to the high-luminance sidewithout using any field memory or any frame memory.

1. A method for driving a solid state image pickup device having aplurality of unit pixel means where each one of the plurality of unitpixel means corresponds to a pixel means having at least one inputconverting section, and CCD electric charge transfer means, the methodcomprising the steps of: setting only a single first signal chargingperiod and only a single second signal charging period for each one ofthe plurality of unit pixel means, where the single second signalcharging period occurs after the single first signal charging period andis shorter than the single first signal charging period; setting thesingle first signal charging period of a first unit pixel means and thesingle first charging period of a second unit pixel means so that thesingle first signal charging periods for the first and second unit pixelmeans have coinciding start times, the first and second unit pixel meansare adjacent to each other in a vertical direction; setting the singlesecond signal charging period of the first unit pixel means and thesingle second signal charging period of the second unit pixel means sothat the single second signal charging periods for the first and secondunit pixel means have different start times and simliar time durationduring which a second signal charge is produced within each unit pixelmeans; and adding the second signal charge of the first unit pixel meansto the second signal charge of the second unit pixel means for output bythe CCD electric charge transfer means.
 2. The method for driving asolid state image pickup device according to claim 1 wherein the secondsignal charging period is controlled using an electronic shutteringoperation.
 3. A method for driving a solid state image pickup devicehaving a plurality of unit pixel means where each one of the pluralityof unit pixel means corresponds to a pixel means having at least oneinput converting section, and CCD electric charge transfer means, themethod comprising the steps of: setting only a single first signalcharging period and only a single second signal charging period for eachone of the plurality of unit pixel means, where the single second signalcharging period occurs after the single first signal charging period andis shorter than the single first signal charging period; setting thesingle second signal charging period of a first unit pixel means and thesingle second signal charging period of a second unit pixel means sothat the single second signal charging periods for the first and secondunit pixel means have different start times and similar time durationduring which a second signal charge is produced within each unit pixelmeans, the first and second unit pixel means are adjacent to each otherin a vertical direction; and adding the second signal charge of thefirst unit pixel means to the second signal charge of the second unitpixel means for output by the CCD electric charge transfer means
 4. Themethod for driving, a solid state image pickup device according to claim3, wherein the second signal charging period is controlled using anelectronic shutteririg operation.
 5. A solid state image pickup devicecomprising: a plurality of unit pixel means arranged in a twodimensional matrix with a horizontal axis and a vertical axis where eachone of said plurality of unit pixel means corresponds to one pixel in animage, each one of said plurality of unit pixel means comprising: (1) atleast one input converting section, (2) CCD electric charge transfermeans, and (3) four transfer electrodes; wherein eight transferelectrodes are provided for two unit pixel means adjacent to each otherin a vertical direction; pulse generating means for driving the eighttransfer electrodes; means for setting a first signal charging periodand a second signal charging period for each one of the plurality ofunit pixel means, where the second signal charging period occurs afterthe first signal charging period and is shorter than the first signalcharging period; means for setting the second signal charging period forthe two unit pixel means which are adjacent to each other in thevertical direction so that the second signal charging period for each ofthe two unit pixel means have different start times and similar timedurations; and means for adding signal charges of the two unit pixelmeans from the second charging periods.
 6. A method for driving a solidstate image pickup device, the method comprising the steps of: (a)setting a first signal charging period and a second signal chargingperiod for each one of a plurality of unit pixel means, the plurality ofunit pixel means being arranged in a matrix with horizontal rows, wherethe second signal charging period is shorter than the first signalcharging period and a first signal charge is produced during the firstsignal charging period and a second signal charge is produced during thesecond signal charging period; wherein the second signal charges ofpairs of unit pixel means which are vertically adjacent are added; (b)enlarging the second signal charge.
 7. The method for driving a solidstate image pickup device according to claim 6, wherein when an electriccharge is transferred using a vertical CCD electric charge transfermeans having four electrodes provided for one unit pixel, the firstsignal charge obtained during the first signal charging period and thesecond signal charge obtained during the second signal charging periodare transferred existing together in said vertical CCD electric chargetransfer means.
 8. The method for driving a solid state image pickupdevice according to claim 6, wherein the second signal charge step (b)is enlarged in proportion to a ratio of the first signal charging periodto the second signal charging period.
 9. The method for driving a solidstate image pickup device according to claim 6, wherein step (b)includes the step of judging whether the first signal charge issaturated or not saturated.